Add the heavy cream and whole milk to the saucepan. Stir to combine and bring to a simmer.
Add Cheese:
Gradually whisk in the grated Parmesan and Romano cheeses until the cheese is fully melted and the sauce is smooth. This should take about 3-5 minutes.
Season the Sauce:
Add salt and pepper to taste. If using, add a pinch of nutmeg for an additional layer of flavor. Continue to simmer for another 2-3 minutes, stirring frequently, until the sauce thickens to your desired consistency.
Serve:
Remove the sauce from heat. Serve immediately over cooked pasta, garnished with fresh parsley if desired.